This invention relates generally to drilling tools having a holder and a cutting blade or bit mounted in the holder.
A drilling plate of this type has become known, for example as the object of DE 3204210C2. A similar technical instruction can also be found in EP 625 395 B1.
The disclosed contents of the two documents will be encompassed in their full scope by the disclosure of the present invention, insofar as it is a matter of explaining the present invention.
In the named drilling plates according to the state of the art, the disadvantage exists that the chip breaker groove of the drilling plate bracket can not be optimally designed because the drilling plate has a uniform thickness and/or plate thickness, seen over its axial length.
This leads to the disadvantage that at the foot side (on the contact surface in the bracket), the drilling plate is just as thick as comparatively on the cutting edge (in the front tip area) and that because of the relatively narrow design of the drilling plate, the drilling plate bracket chip breaker groove is not optimally suited for removing the chips.
In fact, it has been found that this type of drilling plate generates so-called flowing chips, which means that during the drilling process the chips do not break off, but are practically infinitely long. Thus the disadvantage exists that the chips wind around the tool and can only be removed with difficulty.
It is not possible to design the plate so that it is significantly thicker and/or with a greater sheet thickness, in order to apply optimum chip breaker grooves and a chip guiding angle on the bracket of the drilling plate: because of this the bracket would be too thin in the area where the plate is fastened and could break during the drilling procedure.
If an attempt is made to make the plate wider the disadvantage exists that the clamping slot width in the bracket will also have to be enlarged accordingly, which is connected with a weakening of the holding tabs, which therefore can no longer secure the plate optimally against torques that occur. Then there is a danger that these holding tabs in the bracket will break.
On the other hand, it is not possible either to make the known drilling plate thinner in order to apply a corresponding chip breaker groove with a chip guiding angle, since this plate then runs conically inward in the direction of its mounting at its base and designed to be so thin that the danger of breaking the plate exists.
Therefore, the invention is based on the task of further developing a drilling plate of the type named at the beginning that prevents the creation of flowing chips and so that an improved cutting geometry is insured.
A significant characteristic of the invention is that on the front side, two diametrically opposed contact surfaces that are parallel to each other exist which define the base width of the clamping slot in the bracket and that these contact surfaces that are parallel to each other run at an angle and lie opposite the thickness of the cutting edges that enlarge the drilling plate.
Thus the core of the invention is that the drilling plate according to the invention is enlarged over the width of the drilling plate that fits into the clamping slot and contacts there, on the surfaces lying opposite the clamping slot contact surfaces so that enlarged cutting surfaces are formed which now can be designed in an optimum manner with one chip angle and a corresponding chip breaker groove.
Thus in contrast to the state of the art, a drilling plate that is uniformly thick over its entire length is not being described. Rather, according to the invention the drilling plate has a uniform thickness only in the area of the clamping slot and the guide surfaces located there while on the surfaces diametrically opposed to these contact surfaces, the width of the drilling plate (the thickness) is designed so that it is broader in order to have the possibility of applying an optimum cutting geometry in this area for the first time.
To do this, it is provided that corresponding holding tabs diametrically opposed to each other are present in the bracket which between them form the clamping slot in a known way, in which the drilling plate contacts with assigned contact surfaces that are diametrically opposed to each other.
What is now important is that across from these holding tabs, corresponding recess surfaces are provided in the bracket, into which the drilling plate now projects, with expanded cross section which define the cutting geometry.
In this way it is now possible for the first time to insure an optimized cutting geometry because in order to prevent flowing chips, it is provided according to the invention that in the area of the cutting geometry the thickness of the drilling plate is now designed so that it is enlarged in order to apply chip breaker grooves in this area, especially an S-shaped grind of the cutting edges in connection with a chip breaker groove that extends in axial direction.
In addition, clamping the drilling plate in the bracket with two clamping holes having a tapered edge and lying opposite each other is known, which are tensioned with corresponding tapered designed clamping bolts. The clamping is carried out in such a way that when the clamping bolts are tightened, their heads shaped as a cone contact the tapered edge of the respective clamping hole and the drilling plate presses with its base side against the base of the clamping slot.
The object of the present invention now results not only from the object of the individual patent claims, but also from the combination of the individual patent claims with each other.
All the data and characteristics disclosed in the documents including the summary, and in particular the spatial illustration shown in the drawing are claimed as essential to the invention, to the extent that they are novel compared to the state of the art, individually or in combination.